• The side slope of the canal depends upon the type of soil.
  • The canals in alluvial soils are designed assuming a 1/2 :1 side slope, irrespective of the actual initial side slope.
  • It is assumed that after the due course of a run, the canal section would ultimately acquire a 1/2: 1 slope.
  • This happens because silt gets deposited on the berms.
  • Had section been designed with 1/2: 1 slope initially, the section
Table Schedule of Area Statistics and Channel Dimension
Table Schedule of Area Statistics and Channel Dimension
  • would be reduced in due course of time due to silting and the section remaining would be inadequate.
  • As per the recommendation of the Central Water.
  • Power Commission (C.W.P.C.) the side slopes for various soils should be given in Table 19.2.

Table Recommended side slope for Kucha Canals


  • It is a narrow strip of land, left on either side of a channel at G.L., between upper edge of the cut and the inside toe of the bank.
  • The width of the berm depends upon the size of the channel.
  • If canal is in partial cutting, the original width of the berm will be small but it becomes wider after silting over.
  • The berms and side slopes.
  • The canals while constructing area excavated with 1: 1 slope, but after a run, for few months.

The section automatically acquires a side slope of 1/2: 1.

Berm performs the following functions.

  • The width of the canal can be easily increased if required.
  • Slipping soils and boulders are held up at berms and do not allow them to be dropped into the channel.
  • It acts as a storage space for materials if some repair or construction work is to be clone in the canal.
  • Barrow pits may be made on banks for taking soil.
  • These berms get silted up very soon.
  • Such a need for barrow pits arises during canal breaches.
  • They strengthen the channel banks.
  • The rise in water level is marginal with a substantial increase in discharge above the full capacity of the canal.
  • If by mistake excess discharge enters the canal, they do not allow water to rise much and thus a possible breach of the canal is averted.
  • Because of silting of inside edge and top, the terms become impervious, and as such, loss of water by seepage is reduced.
  • Waves developed in the canal do not come in direct contact with the banks and hence possibilities of bank erosion are reduced.
  • They also provide an easy path for inspection.
  • They increase the width of the bank, and thus, the seepage line is not likely to be exposed.
  • For channels in full cutting, a berm of width equal to depth of water is provided at 50 cm above the F.S.L.
  • In channels, partly in cutting, the berm provided is such that after silting its width at F.S.L.
  • Will not exceed twice the depth of water.
  • In channels, fully in an embankment, a berm width varying from twice the depth to thrice the depth is provided at F.S.L.
  • The minimum berm width can also be found out from the Table 19.3.
Table 19.3. Recommended berm width
Table 19.3. Recommended berm width